1. Field of the Invention
The present invention pertains to a process of the preparation of modified polyisocyanurate foams for heat insulation (hereinafter insulation) materials provided by reacting a polyisocyanate in the presence of a carbodiimide catalyst and a trimerization catalyst. More specifically, the present invention relates to the use of aromatic compounds that improve adhesion and compression strengths of the modified foams as well as their friability.
2. Description of the Prior Art
The preparation of modified polyisocyanurate foams containing isocyanurate (a trimer of isocyanate) and carbodiimide linkages is well known in the art as disclosed by U.S. Pat. No. 3,657,161. Further arts such as U.S. Pat. Nos. 3,894,972; 3,928,256; 3,981,829; 3,998,766; and 4,166,164 disclose other well known catalysts: (i) furfuryl alcohols and a tertiary amine trimerization catalyst, (ii) a co-catalyst system of tertiary aminoalcohols and a tertiary amine trimerization catalyst, (iii) a catalyst system comprising alkanol amino triazine, hexahydrotriazine, and phenol or substituted phenol, (iv) oxyalkylated Mannich polyols, and (v) C.sub.1 -C.sub.8 alkali metal carboxylates as trimerization catalysts.
In general, the modified polyisocyanurate foams produced in these preparations have high friability and poor flame-retardancy for insulation materials. Thus phosphorous compounds containing active hydrogen have been employed to improve the flame-retardancy of the foams, as disclosed in U.S. Pat. No. 3,994,893. The use of toluene diisocyanate has been employed in order to improve the friability and flame-retardancy of the foams and is described in U.S. Pat. No. 3,994,837.
In the foregoing preparations, chlorofluorocarbons were used as blowing agents. However, due to the prohibited use of chlorofluorocarbons in the near future, processes of the preparation of the foams without the use of chlorofluorocarbons have been proposed in the arts, as disclosed by European Patent Publication EP 0381 324 A1 and U.S. Pat. No. 5,126,305. These arts describe the use of phospholene oxides as carbodiimide catalysts and water so as to form carbon dioxide as a blowing agent. Unfortunately, the employment of water brings urea linkages which are spread unevenly and cause coagulation or domain in the foams. Thus the foams provided by these processes were friable and possessed insufficient adhesion strength for insulation materials.